The proposed work will continue investigation of the properties of S-substituted isothiazolidinium salts. These salts are formed upon oxidation by iodine of compounds containing a primary or secondary amine functional group separated by a trimethylene bridge from a thioether sulfur (y-NH2-(CH2)3-S-CH3). We have been able to prepare a series of compounds with y being variously substituted phenyl and benzyl groups. This will permit a systematic probing of the reactivity and stability of the N-S bond as function of the substituent on the phenyl ring of y. To be investigated are the kinetics of the formation reaction and the hydrolysis of the isothiazolidinium salts under acid and base conditions.